In many applications it is important to measure accurately the volume of liquid passing through a pipe or tube, for example a fuel dispenser, such as a petrol pump. If the liquid is contaminated with gas, such as air, vapour and/or other gas, the meter, which cannot differentiate between the liquid and the gas, will produce an erroneous reading for the volume of liquid dispensed. Thus the purchaser of the fuel will pay not only for the fuel actually dispensed, but also for any gas entrained in the fuel flow line.
It is known, for example from Australian Patent No. 460441, to provide a device in the fuel flow line to separate the gas from the liquid by arranging for the liquid to flow through a separation tank, located upstream of the meter, in which any gas can rise to the top and from which liquid is drawn from the bottom. Exit of liquid out of the tank is via a main valve which is controlled either by a pilot valve or by an orifice to close the main valve when there is a substantial volume of gas in the tank. This gas escapes from the tank via a vent passage to an air separation sump, the tank replacing the escaping gas with further liquid or liquid/gas mixture. When the pilot valve or orifice sense that the liquid/gas mixture in the tank has again reached a certain level, the main valve is opened to allow liquid to flow at normal operating levels.
Although the above-described device works reasonably well, it needs to be built into the liquid dispensing system with the various valves and the orifice being interconnected by pipes or hoses which requires a substantial investment and a relatively large amount of space.